1. Field of the Invention
The present invention relates to apparatus and methods for disposing a thermal interface material between a heat source and a heat dissipation device. In particular, the present invention relates to a microelectronic package comprising a heat dissipation device having an inlet over a back surface of a microelectronic device and an outlet away from the microelectronic device back surface, wherein the thermal interface material is disposed between the heat dissipation device and the microelectronic device through the inlet.
2. State of the Art
Higher performance, lower cost, increased miniaturization of integrated circuit components, and greater packaging densities of integrated circuits are ongoing goals of the microelectronic industry. As these goals are achieved, microelectronic dice become smaller. Accordingly, the density of power consumption of the integrated circuit components in the microelectronic device has increased, which, in turn, increases the average junction temperature of the microelectronic device. If the temperature of the microelectronic device becomes too high, the integrated circuits of the microelectronic device may be damaged or destroyed.
Various apparatus and techniques have been used and are presently being used for removing heat from microelectronic devices. One such heat dissipation technique involves the attachment of a heat dissipation device to a microelectronic device. FIG. 9 illustrates an assembly 200 comprising a microelectronic device 202 (illustrated as a flip chip) physically and electrically attached by an active surface 204 thereof to a first surface 206 of a carrier substrate 208 by a first plurality of interconnects 212, such as solder balls. An underfill material 214 may be disposed between the microelectronic device active surface 204 and the carrier substrate 208. A second plurality of interconnects 216 may be attached to a second surface 218 of said carrier substrate 208 for connection to external components (not shown).
An interior surface 224 of a heat dissipation device 226 may be attached to a back surface 228 of the microelectronic device 202 by a thermal interface material 232, such as thermally conductive adhesive or solder. The heat dissipation device 226 may further comprise a lip portion 234 extending toward and attached to the carrier substrate 208 with an adhesive material 236, such as epoxies, urethane, polyurethane, silicone elastomers, and the like. The heat dissipation device 226 may be constructed from a thermally conductive material, such as copper, copper alloys, aluminum, aluminum alloys, and the like.
However, the disposition of the thermal interface material 232 between the microelectronic device 202 and the heat dissipation device 226 is a difficult process. FIG. 10 illustrates a known process for disposing the thermal interface material. The thermal interface material is placed as pre-formed sheet 242 between the microelectronic device back surface 228 and the heat dissipation device interior surface 224. The assembly is then pressurized (first force 244 on the heat dissipation device 226 and/or second force 246 on the microelectronic device 202) while being heated, such as in an oven, which melts the thermal interface material pre-formed sheet 242 and adheres it to the heat dissipation device 226 and the microelectronic device 202. Unfortunately, this process can easily trap air pockets or voids 248 between the thermal interface material pre-formed sheet 242 and the heat dissipation device interior surface 224, and/or the thermal interface material pre-formed sheet 242 and the microelectronic device back surface 228. The voids 248 greatly reduce the heat transfer from the microelectronic device 202, as will be understood to those skilled in the art.
FIGS. 11 and 12 show methods of forming a void-free thermal interface. FIG. 11 illustrates one method which comprises placing a liquid thermal interface material 252 on an edge 254 of a gap 256 between the heat dissipation device interior surface 224 and the microelectronic device back surface 228. The liquid thermal interface material 252 is drawn into the gap 256 in direction 258 by capillary action. One way to achieve this is dip the edge 254 into a solder bath. However, as it is understood by those skilled in the art, it is difficult to apply this method to the assembly, as shown in FIG. 9, due to the larger sizes of the heat dissipation device 226 and carrier substrate 208, relative to the microelectronic device 202.
FIG. 12 illustrates another method which comprises placing a small, thick thermal interface material globule 262 between the heat dissipation device interior surface 224 and the microelectronic device back surface 228 at or near a center of the microelectronic device back surface 228. The thermal interface material globule 262 is then heated, such as in an over, so that it becomes flowable and a first force 264 is placed on the heat dissipation device 226 and/or second force 266 is placed on the microelectronic device 202, such that the thermal interface material 262 is dispersed across the microelectronic device back surface 228. This method can be used in situations were the microelectronic device 202 is small (i.e., small bonding applications). However, for microelectronic devices 202 larger than about 300 mils in length, this method becomes ineffective, as the thermal interface material may not extend to the edges of the microelectronic device 202 without considerable pressure and/or temperature.
Therefore, it would be advantageous to develop an improved method and related apparatus for dispersing a thermal interface material between a microelectronic device and a heat dissipation device.